UN Special Envoy to the Middle East: 'I leave the Gaza Strip in an even worse situation than before'

WHO reports more than 1,000 cases in 21 countries

World Health Organisation chief Margaret Chan has warned against complacency regarding H1N1 influenza. She said a second wave of the virus would "be the biggest of all outbreaks... in the 21st century". Portugal reported its first confirmed case.

AFP - The World Health Organisation chief warned Monday that swine flu could return with a vengeance despite Mexico's President Felipe Calderon insisting his country has contained the epidemic.

WHO chief Margaret Chan said that a second wave of the virus "would be the biggest of all outbreaks the world has faced in the 21st century", puncturing optimism emanating from the outbreak's epicentre.

Diplomatic damage from the epidemic also reverberated with China denying it had discriminated against Mexican nationals after dozens were placed under quarantine over the weekend despite showing no signs of the flu.

Twenty-five people have died from swine flu, according to the WHO, all but one of them in Mexico. Twenty-one countries have confirmed cases of the virus which has affected around 900 people.

Calderon said Mexico had managed "to contain the epidemic" and was now "in a position to overcome" the A(H1N1) virus.

Mexico's Health Minister Jose Angel Cordova said the epidemic peaked between April 23 and 28 and was "in its phase of decline".

But Chan said the end of the flu season in the northern hemisphere meant that while any initial outbreak could be milder, a second wave could be more lethal, reflecting a pattern seen with the 1918 Spanish flu pandemic that killed up to 50 million people.

"We hope the virus fizzles out, because if it doesn't we are heading for a big outbreak," Chan told the Financial Times in an interview, adding it could re-emerge in the months ahead "with a vengeance".

"I'm not predicting the pandemic will blow up, but if I miss it and we don't prepare, I fail. I'd rather over-prepare than not prepare."

The UN agency last week raised its alert level to five, one a scale of one to six, indicating a global pandemic is imminent.

In an interview with Spain's El Pais newspaper, Chan said it was important to avoid a "wave of panic" if the alert level was raised to the maximum six, adding that such a move would not mean "the end of the world".

More countries are confirming cases every day with Portugal the latest to join the list, while France announced two new confirmed cases as did Italy, doubling its previous caseload.

Japan tripled the number of quarantine officers at Tokyo's Narita airport to try to detect cases at the start of a holiday week.

In the United States, the only other country to have recorded a death from the virus, officials said 30 of the 50 states had now confirmed cases.

US Health and Human Services Secretary Kathleen Sebelius echoed Chan's warning that the real test would come when the winter flu season hits.

"Even if this current situation seems to be lessening, if we are cautiously optimistic, we really don't know what's going to happen when real flu season hits (together) with H1N1 virus," she told CBS television.

In China, centre of the 2003 SARS outbreak, authorities have been accused of discriminating against Mexicans in a bid to keep out the virus.

Although no case of swine flu has been reported on mainland China, one Mexican who stayed in a hotel in Hong Kong has tested positive.

A Mexican embassy official in Beijing said nearly 70 Mexicans had been quarantined across China including in Beijing, Shanghai and the southern city of Guangzhou even though they had no flu symptoms.

China's foreign ministry said in a statement: "The relevant measures are not directed at Mexican citizens and are not discriminatory."

Russia's food safety agency meanwhile extended a ban on all meat imports to a fourth US state and banned pork products from Spain and parts of Canada.

The veterinary and food safety agency announced the extension despite an appeal by the United States, Canada, Mexico that there was no scientfic justification.

Egypt also pushed ahead with a mass slaughter of the country's quarter of a million pigs, a day after clashes erupted with protesting pig farmers.

Police were deployed in force around the Cairo slum district of Manshiyet Nasr where hundreds of residents, mostly Coptic Christian rubbish recyclers, on Sunday fought running battles with police firing tear gas and rubber bullets.